Frequently Asked Questions

What is Transportation Demand Model?

It is a collection of data files and computer programs that are combined to forecast highway traffic volumes, transit ridership and other aspects of the transportation system.

How far into the future do these forecasts look?

The model forecast years range from 10 to 25 years from today.

Who uses the model results?

The model primarily serves SCAG planners who maintain two major planning documents: the Regional Transportation Plan and the Regional Transportation Improvement Program. The results also support planners within SCAG and at other agencies conducting transportation major investment studies.

Do other agencies have their own transportation demand models?

Yes. In Southern California Caltrans, MTA, OCTA and Los Angeles City DOT maintain their own demand models. All major urban areas have long range transportation plans maintained by their respective metropolitan planning organization (MPO). SCAG, MTC and SANDAG are the MPO’s for Southern California, the San Francisco Bay Area, and San Diego respectively.

Can the model predict the best route for my drive home?

No. The model is used for long-range forecasting. The model does not have information on traffic accidents or temporary road closures that could impact your commute.

How accurate are these forecasts?

The SCAG model is designed to cover almost all of Southern California. It is validated against current year traffic counts and patronage checks in order to provide reasonable estimates for major arterials and transit corridors. Because the model is used for long-range forecasts (10 to 25 years) it is not possible to validate the results directly. Instead a peer review panel is convened to assure that a model conforms to recognized modeling practice.